1. Field of the Invention
A first aspect of the invention relates to a method and a device for measuring the intensity of a light beam provided by a light source.
2. Description of Related Art
A second aspect of the invention relates to a method and a device for regulating a light source.
In the following specification and claims, xe2x80x9clightxe2x80x9d means any electromagnetic radiation at least in the spectrum of visible light, infrared and ultraviolet. A somewhat similar device is known from U.S. Pat. No. 5,489,771. The light beam emerging from a light source passes through a diffuser block, and a small portion of light directed to a measuring photodiode at the side of the diffuser block forms the basis for measurement of the intensity of the light beam. However, it is not warranted that the portion of light directed to the measuring photodiode is really representative for the intensity of the whole light beam. Much light which is deflected to the side is lost. It is difficult to properly measure the output intensity of a light beam of which the wavelength is corrected. The prior measuring system comprises at least two separate constituents, namely the diffuser and the photodiode.
A first aim of the instant invention is to provide a method and a device which makes possible to avoid the above drawbacks and to provide a compact, inexpensive measuring device.
The above mentioned first aim is addressed by a device for measuring a spatially averaged intensity of a light beam. This device comprises an electrically non-conducting support having a surface, and a photoelectric element. The photoelectric element comprises an array of spatially distributed photoelectric members that are electrically connected with each other. The array is applied to the surface of the support. Furthermore, the array of photoelectric members is adapted to receive and measure the intensity of a light beam directed towards the surface of the support. Each of the photoelectric members of the array has a surface adapted to receive, but not to transmit light. The surface of the support comprises a first set of areas and a second set of areas. Each of the first set of areas is covered by one of the photoelectric members and, therefore, does not allow light transmission. None of the second set of areas is covered by a photoelectric member and each of these areas allows light transmission. Each of the areas of the second set of areas is located between two or more of the areas of the first set of areas.
A method according to the invention for addressing the above mentioned first aim measures the spatially averaged intensity of a light beam provided by a light source. A photoelectric element is positioned into a light beam emerging from a light source. The photoelectric element comprises an array of spatially distributed photoelectric members which are applied to a surface of an electrically non-conducting support. The photoelectric members are electrically connected to one another. Each of the photoelectric members of the array has a surface adapted to receive, but not to transmit light. Also, the surface of the support comprises areas which allow light transmission. Each of these areas being located between at least two areas of the support surface which are covered by the photoelectric members. The intensity of the light beam provided by the light source is then measured by means of the photoelectric element.
In a first preferred embodiment of the invention, a light beam directly passes through a photoelectric module which serves at the same time in an optimum manner for transmission and measurement of the light beam. For this purpose the latter photoelectric module comprises an at least partially transparent support and a photoelectric element applied to, laid over or disposed on a surface of that support, which photoelectric element comprises at least one member, and preferably an array of photoelectric members, which is/are spatially distributed over the surface of the support and over the cross section of the light beam respectively. When a light beam passes through the above mentioned photoelectric module, the above mentioned photoelectric element properly measures the averaged power or intensity of the light beam. The transparent or semi-transparent support may directly serve as a beam-shaping element, wavelength filter, polarizer, or a combination thereof. The photoelectric element properly measures the intensity of the modified light emerging from the photoelectric module. The expression xe2x80x9clight beam passes through the photoelectric elementxe2x80x9d means that light passes through the support, on a surface of which the photoelectric element is disposed, and between the above mentioned, spatially distributed members of the photoelectric element. Due to the double function mentioned above of a device according to the invention built as a unitary module, this module is simple and compact and may easily be assembled with other parts of any other suitable device. The design allows a high flexibility of the shape of the spatially distributed photoelectric element, which is e.g. a grid-shaped photoelectric element, the grid-shape having a suitable pattern. Multiple uses of a device according to the invention are therefore possible.
As pointed out at the outset a second aspect of the invention relates to a method and a device for regulating a light source. A device of this kind is known for instance from U.S. Pat. No. 4,998,043. In this prior device the light beam from a light emitting diode (LED) is split up in a beam splitter and the partial beam thereby split off is directed to a photodiode PD. The measuring signal produced by means of the photodiode is fed back to a comparator serving as a control or regulating circuit of which the output controls a drive circuit for regulating the power fed to the LED in order to keep the light emission by this LED at a constant level. Such a regulating system is of particular importance when a LED is used as a light source since the characteristics of LEDs are known to be subject to high lot-to-lot variations, aging effects, low temperature stability of the spectral properties and of the light intensity and low homogeneity of the spatial spectrum. The prior device mentioned above is quite complicated due to the use of a beam splitter in a fiber optics system, and simple compact and inexpensive integration thereof is not warranted.
A second aim of the instant invention is therefore to provide a method and a device for measuring the spatially averaged intensity of a light beam by means of compact and low-cost means, without fiber optics and with high luminous efficiency.
This above mentioned second aim is addressed with a device for regulating the intensity of a light beam provided by a light source. The device comprises a photoelectric element by means of which the intensity of the light beam is measured, and a driving circuit for regulating the output power of the light source by feedback of a measuring signal provided by the photoelectric element to the driving circuit. The device is characterized in that the photoelectric element is located in the path of the light beam provided by the light source and the photoelectric element comprises an array of spatially distributed photoelectric members. The array of spatially distributed photoelectric members is applied to a surface of an electrically non-conducting support and is electrically connected to one another. Each of the photoelectric members of the array has a surface adapted to receive, but not to transmit light. The surface of the support comprises areas that allow light transmission, each of the latter areas being located between at least two areas of the support surface that are covered by the photoelectric members.
A method according to the invention for addressing the above mentioned second aim regulates a light source. The intensity of the light beam provided by the light source is measured by means of a photoelectric element located in the path of the light beam provided by the light source in order to generate a measuring signal representative of the intensity. The photoelectric element comprises an array of spatially distributed photoelectric members which are applied to a surface of an electrically non-conducting support and which are electrically connected to one another. Each of the photoelectric members of the array has a surface adapted to receive, but not to transmit light. The surface of the support comprises areas which allow light transmission, each of the latter areas being located between at least two areas of the support surface which are covered by the photoelectric members. The intensity of the light beam provided by the light source is regulated by means of a driving circuit. This regulating step includes feedback of the measuring signal provided by the photoelectric element to the driving circuit.